Fetal Alloimmune Thrombocytopenia: An Overview

Introduction:

Fetal alloimmune thrombocytopenia is a disease associated with the immune system. It is a rare disease that develops when the mother’s blood gets exposed to that of the baby. The term ‘alloimmune’ implies the type of immune response against the antigens (the substances that result in the production of antibodies) from the same species members. Thrombocytopenia is a condition when the level of platelet cells or thrombocytes (a type of blood cell) in the bloodstream decreases.

What Is Fetal Alloimmune Thrombocytopenia?

Fetal alloimmune thrombocytopenia is an uncommon disease and causes a worse form of thrombocytopenia (a decreased platelet count in the blood) in newborns. It may lead to extreme complications, which can progress to long-term conditions. Fetal alloimmune thrombocytopenia is a rare disease associated with impaired immunity. In this case, the immune cells in the mother’s blood attack the platelet cells in the baby’s bloodstream. The immune system usually gets activated when a foreign body gets identified. In the case of fetal alloimmune thrombocytopenia, the platelet cells in the baby's bloodstream are recognized as foreign bodies. As a result, antibodies are produced and released in the mother's body to attack them. During the fetal development within the uterus or delivery period, the maternal blood gets exposed to the baby's blood, developing the immune response associated with fetal alloimmune thrombocytopenia.

Fetal alloimmune thrombocytopenia is also called by the following names:

• Neonatal alloimmune thrombocytopenia (NAIT).

• Fetal and neonatal alloimmune thrombocytopenia (FNAIT).

• Fetomaternal alloimmune thrombocytopenia (FMAIT).

How Is Fetal Alloimmune Thrombocytopenia Developed?

When a foreign substance or antigen enters the body, the immune system identifies or recognizes these antigens and releases antibodies or immunoglobulin (proteins that protect from unwanted foreign substances). These antibodies fight against the antigens to eliminate them from the body. The platelets in the baby's bloodstream will be identified as a foreign substance by the mother's body when the platelets in both their bloodstream are different. This happens when the corresponding genes are inherited from the father. Platelets are responsible for clot formation. Attacking the platelets in the baby’s bloodstream decreases their count (thrombocytopenia), leading to bleeding and blood vessel rupture. Thrombocytopenia may be due to increased destruction or reduced formation of the platelets.

What Are the Signs and Symptoms of Fetal Alloimmune Thrombocytopenia?

The signs and symptoms of fetal alloimmune thrombocytopenia depend on the platelet count in the baby’s bloodstream. The following are some common signs of the condition, which may show up within four weeks after birth or in the fetal stage:

• Tiny brown to purple colored spots of bleeding may develop under the skin. This is called petechiae.

• Purple-colored flat spots or rash-like lesions may be found on the skin. This lesion is called purpura and may be due to the leakage of blood from small blood vessels.

• A few hours after the birth, the baby's skin may show bruising or hematoma (discoloration due to blood collection around the large blood vessels under the skin).

The symptoms mentioned above will be developed in case of mild to moderate fetal alloimmune thrombocytopenia. The discolorations will fade away after treatment. The following are the symptoms of severe fetal alloimmune thrombocytopenia:

• Intracranial Hemorrhage: Intracranial hemorrhage, also called brain bleeding or brain hemorrhage, is the bleeding in the intracranial vault.

• Gastrointestinal Hemorrhage: It is bleeding within the gastrointestinal tract.

• Pulmonary Hemorrhage: Pulmonary hemorrhage is the bleeding within the lungs.

• Hyphema: Bleeding in the eye or hyphema may also develop in severe cases of fetal alloimmune thrombocytopenia.

• Cephalohematoma: Blood accumulation between the skull and scalp of the newborn is called cephalohematoma. Cephalohematoma can lead to brain damage and long-term neurological conditions.

• Long-Term Disability: Severe bleeding within the organs can lead to long-term disabilities in the affected child.

• Death: It can also lead to death in severe cases.

Long-term neurological conditions that could develop in case of severe fetal alloimmune thrombocytopenia include the following:

• Cerebral Palsy: Cerebral palsy is a congenital condition affecting balance, posture, muscle tone, and movement. Abnormal brain development leads to the condition.

• Intellectual Disability: Intellectual disability is when cognitive skills, functioning, and practical skills are impaired. In such cases, the person's intelligence quotient will be below average, lacking the required life skills.

• Seizures: Seizure refers to abnormal and uncontrollable jerking movements due to sudden and unexpected changes in the electrical activity within the brain.

• Bilateral Sensorineural Hearing Loss: The hair cells within the inner ear get damaged in case of sensorineural hearing loss. This impairs the transmission of sound waves to the brain and leads to hearing loss. Both ears get affected if the condition is bilateral.

How to Diagnose Fetal Alloimmune Thrombocytopenia?

Fetal alloimmune thrombocytopenia mostly remains underdiagnosed during pregnancy screening tests. In most cases, it gets diagnosed with a second child during pregnancy due to its presence in the first child. But in the case of the first pregnancy, it remains undiagnosed during pregnancy. Further testing done after birth helps to diagnose the condition. The healthcare provider will learn about the condition by observing the apparent skin lesions or discoloration. The following are some tests that help diagnose the condition:

• Maternal Antibody Testing: Testing the mother’s serum for HPA (human platelet antigens) antibodies is a helpful tool to detect fetal alloimmune thrombocytopenia. HPAs can trigger the generation of alloantibodies when they come in contact with foreign platelets carrying different HPAs. The presence of HPA antibodies in the maternal serum indicates that the chances of fetal alloimmune thrombocytopenia are high.

• Human Platelet Antigen Genotyping: The chances of intracranial hemorrhage and fetal thrombocytopenia can be assessed with the help of HPA genotyping. This helps in detecting the presence of HPA genes.

How Is Fetal Alloimmune Thrombocytopenia Treated?

The following are the standard therapies or treatments done to the baby in the case of fetal alloimmune thrombocytopenia:

• Platelet Transfusion: Platelets will be transfused to the baby to compensate for the destroyed platelets and to maintain the average count.

• Intravenous Immunoglobulin Therapy: This will be done to the mother when the fetus has the chance of having neonatal alloimmune thrombocytopenia.

• Intravenous Steroid Therapy: Intravenous steroid therapy given to the mother during pregnancy decreases the production of antibodies responsible for fetal alloimmune thrombocytopenia.

• Serial Intrauterine Platelet Transfusion: Platelets will be transfused to the fetus in this method.

Conclusion:

Fetal alloimmune thrombocytopenia is a rare disease in which the platelet count is decreased in the blood of the fetus or the newborn. It may lead to long-term complications in the baby. In mild form, the skin may exhibit discolored lesions. In severe cases, bleeding within multiple organs will lead to life-threatening results.